This adds a kfunc wrapper around strncpy_from_user,
which can be called from sleepable BPF programs.
This matches the non-sleepable 'bpf_probe_read_user_str'
helper except it includes an additional 'flags'
param, which allows consumers to clear the entire
destination buffer on success or failure.
Signed-off-by: Jordan Rome <linux@xxxxxxxxxxxxxx>
---
include/uapi/linux/bpf.h | 9 ++++++++
kernel/bpf/helpers.c | 42 ++++++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 9 ++++++++
3 files changed, 60 insertions(+)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e05b39e39c3f..d3b69cb055c0 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7513,4 +7513,13 @@ struct bpf_iter_num {
__u64 __opaque[1];
} __attribute__((aligned(8)));
+/*
+ * Flags to control bpf_copy_from_user_str() behaviour.
+ * - BPF_F_PAD_ZEROS: Pad destination buffer with zeros. (See the respective
+ * helper documentation for details.)
+ */
+enum {
+ BPF_F_PAD_ZEROS = (1ULL << 0)
+};
+
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index d02ae323996b..e5614a980d59 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2939,6 +2939,47 @@ __bpf_kfunc void bpf_iter_bits_destroy(struct bpf_iter_bits *it)
bpf_mem_free(&bpf_global_ma, kit->bits);
}
+/**
+ * bpf_copy_from_user_str() - Copy a string from an unsafe user address
+ * @dst: Destination address, in kernel space. This buffer must be at
+ * least @dst__szk bytes long.
+ * @dst__szk: Maximum number of bytes to copy, including the trailing NUL.
+ * @unsafe_ptr__ign: Source address, in user space.
+ * @flags: The only supported flag is BPF_F_PAD_ZEROS
+ *
+ * Copies a NUL-terminated string from userspace to BPF space. If user string is
+ * too long this will still ensure zero termination in the dst buffer unless
+ * buffer size is 0.
+ *
+ * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
+ * memset all of @dst on failure.
+ */
+__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
+{
+ int ret;
+
+ if (unlikely(flags & ~BPF_F_PAD_ZEROS))
+ return -EINVAL;
+
+ if (unlikely(!dst__szk))
+ return 0;
+
+ ret = strncpy_from_user(dst, unsafe_ptr__ign, dst__szk - 1);
+ if (ret < 0) {
+ if (flags & BPF_F_PAD_ZEROS)
+ memset((char *)dst, 0, dst__szk);
+
+ return ret;
+ }
+
+ if (flags & BPF_F_PAD_ZEROS)
+ memset((char *)dst + ret, 0, dst__szk - ret);
+ else
+ ((char *)dst)[ret] = '\0';
+
+ return ret + 1;
+}
+
__bpf_kfunc_end_defs();
BTF_KFUNCS_START(generic_btf_ids)
@@ -3024,6 +3065,7 @@ BTF_ID_FLAGS(func, bpf_preempt_enable)
BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)
BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
BTF_KFUNCS_END(common_btf_ids)
static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e05b39e39c3f..d3b69cb055c0 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7513,4 +7513,13 @@ struct bpf_iter_num {
__u64 __opaque[1];
} __attribute__((aligned(8)));
+/*
+ * Flags to control bpf_copy_from_user_str() behaviour.
+ * - BPF_F_PAD_ZEROS: Pad destination buffer with zeros. (See the respective
+ * helper documentation for details.)
+ */
+enum {
+ BPF_F_PAD_ZEROS = (1ULL << 0)
+};
+
#endif /* _UAPI__LINUX_BPF_H__ */
--
2.43.5
